Pressure Responses of Tourniquet Practice Models to Calibrated Force Applications.

BACKGROUND: Tourniquet training sometimes involves models, and a certification process is expected to use something other than human limbs; therefore, investigating model- and limb-pressure responses to force application is important. METHODS: Pressure response to force was collected for a 3.8cm-wide nonelastic strap and a 10.1cm-wide elastic strap placed over 14 objects. Each object was suspended; an inflated neonatal blood pressure cuff was placed atop the object with the strap over the bladder; and strap ends were connected below with 4.54kg weights attached at 20-second intervals to 27.24kg. RESULTS: Pressure-response curves differed by strap, thigh aspect (medial, lateral, ventral, dorsal; n = 2 subjects; p < .0001); subject (medial thigh; n = 3 subjects; p < .0001); and object (thighs; small and large pool noodles ± central metal rod, foam yoga roller, coffee can, 20% ballistic gel cylinder [Gel; Clear Ballistics; clearballistics.com] with central metal tubing, rolled pair of 5mm yoga mats ± central metal rod, hemorrhage-control training thigh [Z-Medica], sand-filled training manikin limb [Drumm Emergency Solutions]; p < .0001). Compliance, circumference, support techniques, and surface interactions, especially with the 10.1cm-wide elastic strap, affected pressure responses: smaller circumference, lower compliance, and lower surface coefficient of friction were associated with higher pressure/force applied. CONCLUSIONS: Different objects have different pressure-response curves. This may be important to acquisition and retention of limb tourniquet skills and is important for systems for certifying tourniquets.

Limb Position Change Affects Tourniquet Pressure.

BACKGROUND: Limb position changes are likely during transport from injury location to definitive care. This study investigated passive limb position change effects on tourniquet pressure and occlusion. METHODS: Triplicate buddy-applied OMNA® Marine Tourniquet applications to Doppler-based occlusion were done to sitting and laying supine mid-thigh (n=5) and sitting mid-arm (n=3). Tourniqueted limb positions were bent/straight/bent and straight/bent/straight (randomized first position order, 5 seconds/position, pressure every 0.1 second, two-way repeated measures ANOVA). RESULTS: Sitting thigh occlusion pressures leg bent were higher than straight (median, minimum-maximum; 328, 307-403mmHg versus 312, 295-387mmHg, p = .013). In each recipient, the pressure change for each position change for each limb had p < .003. In each recipient, when sitting, leg bent to straight increased pressure (326, 276-415mmHg to 371, 308-427mmHg bent first and 275, 233-354mmHg to 311, 241-353mmHg straight first), and straight to bent decreased pressure (371, 308-427mmHg to 301, 262-388mmHg bent first and 312, 265-395mmHg to 275, 233-354mmHg straight first). When laying, position changes from leg bent first resulted in pressure changes in each recipient but not in the same directions in each recipient. From laying leg straight first, in each recipient changing to bent increased the pressure (295, 210-366mmHg to 328, 255-376mmHg) and to straight decreased the pressure (328, 255-376 mmHg to 259, 210-333 mmHg). Sitting arm bent occlusion pressures were lower than straight (230, 228-252mmHg versus 256, 250-287mmHg, p = .026). Arm position changes resulted in pressure changes in each recipient but not in the same directions in each recipient. Changes in pressure trace character (presence or absence of rhythmically pulsatile traces) and Doppler-based occlusion were consistent with limb position-induced changes in tourniquet pressure (each p ≤ .001 leg, p = .071 arm traces, and p = .188 arm occlusion). CONCLUSIONS: Passive limb position changes can cause significant changes in tourniquet pressure. Therefore, tourniquet adequacy should be reassessed after any limb position change.

OMNA Marine Tourniquet Self-Application.

BACKGROUND: The OMNA Marine Tourniquet is a 5.1cm-wide, simple redirect buckle, hoop-and-loop secured, ratcheting tourniquet designed for storage and use in marine environments. This study evaluated self-application effectiveness and pressures. METHODS: Triplicate secured, occlusion, and completion pressures were measured during 60 subjects pulling down or up thigh applications and nondominant, single-handed arm applications. Arm pressure measurements required circumferences =30cm. RESULTS: Thirty-one subjects had arm circumferences ≥30cm. All 540 applications were effective; 376 of 453 applications had known secured pressures >150mmHg (89 of 93 arm). Thigh down versus up pulling directions were not different (secured, occlusion, and completion pressures and ladder tooth advances). Occlusion pressures were 348mmHg (275-521mmHg) for combined thighs and 285mmHg (211-372mmHg) for arms. Completion pressures were 414mmHg (320-588mmHg) for combined thighs and 344mmHg (261-404mmHg) for arms. Correlations between secured pressures and occlusion ladder tooth advances (clicks) were r2 = 0.44 for combined thighs and 0.68 for arms. Correlations between occlusion pressures and occlusion clicks were poor (r2 = 0.24, P < .0001 for combined thighs and r2 = 0.027, P = .38 for arms). CONCLUSIONS: The OMNA Marine Tourniquet can be self-applied effectively, including one-handed applications. Occlusion and completion pressures are similar to reported 3.8cm-wide Ratcheting Medical Tourniquet pressures.

Clothing Effects on Limb Tourniquet Application.

BACKGROUND: Sometimes tourniquets are applied over clothing. This study explored clothing effects on pressures and application process. METHODS: Generation 7 Combat Application Tourniquets (C-A-T7), Generation 3 SOF® Tactical Tourniquets-Wide (SOFTTW), Tactical Ratcheting Medical Tourniquets (Tac RMT), and Stretch Wrap And Tuck Tourniquets (SWATT) were used with different clothing conditions (Bare, Scrubs, Uniform, Tights) mid-thigh and on models (ballistic gel and yoga mats). RESULTS: Clothing affected pressure responses to controlled force applications (weight hangs, n=5 thighs and models, nonlinear curve fitting, p < .05). On models, clothing affected secured pressures by altering surface interactions (medians: Gel Bare C-A-T7 247mmHg, SOFTTW 99mmHg, Tac RMT 101mmHg versus Gel Clothing C-A-T7 331mmHg, SOFTTW 170mmHg, Tac RMT 148mmHg; Mats Bare C-A-T7 246mmHg, SOFTTW 121mmHg, Tac RMT 99mmHg versus Mats Clothing C-A-T7 278mmHg, SOFTTW 145mmHg, Tac RMT 138mmHg). On thighs, clothing did not significantly influence secured pressures (n=15 kneeling appliers, n=15 standing appliers) or occlusion and completion pressures (n=15). Eleven of 15 appliers reported securing on clothing as most difficult. Fourteen of 15 reported complete applications on clothing as most difficult. CONCLUSIONS: Clothing will not necessarily affect tourniquet pressures. Surface to tourniquet interactions affect the ease of strap sliding, so concern should still exist as to whether applications over clothing are dislodged in a distal direction more easily than applications on skin.

Characterizing a System for Measuring Limb Tourniquet Pressures.

BACKGROUND: Pressure is an important variable in emergency use limb tourniquet science. This study characterizes one system for measuring tourniquet-applied pressure. METHODS: A neonatal blood pressure cuff bladder was inflated to target pressures over atmospheric. Unconstrained or constrained within 1-inch tubular polyester webbing, the neonatal cuff was placed in a 500mL Erlenmeyer flask. A 3-hole stopper provided connections to flask interior (chamber) and bladder pressure sensors and a 60mL syringe for altering chamber pressure: atmospheric to >1500mmHg absolute to atmospheric. RESULTS: Within a finite range of chamber pressures, the neonatal cuffbased system accurately indicates applied pressure (minimum and maximum 95% confidence interval linear regression slopes of 0.9871 to 0.9953 and y-intercepts of -0.1144 to 2.157). The visually defined linear response ranges for bladder inflation pressures were as follows for unconstrained/ constrained: 100 to 400mmHg unconstrained/450mmHg constrained for 10mmHg, 150 unconstrained/100 constrained to 450mmHg for 12mmHg, 150 to 500mmHg for 15mmHg, 150 to 500mmHg unconstrained/550mmHg constrained for 18mmHg, 150 to 550mmHg for 21mmHg. Below the linear response range, the inflated bladder system indicated higher pressures than chamber pressures. Above the linear response range, the system indicated progressively lower pressures than chamber pressures. CONCLUSIONS: Within the linear response range, the bladder pressure accurately indicates surface-applied pressure.